Objectives of this study are to explore the possible role of a transmissible agent recently isolated in our laboratory in the etiology of Crohn's Disease. Cocultivation of preparations of resected intesting from patients with Crohn's Disease with human embryonic lung fibroblasts has yielded an agent which produces cytopathic effect after one week of culture. The agent has been passed up to six times in cell cultures and serum from patients with Crohn's Disease has been shown to inhibit the cytopathic change. Hyperimmune serum which neutralizes several of the isolates has been produced in guinea pigs. We propose to study the incidence of this antigen in resected specimens from patients with Crohn's Disease, ulcerative colitis, diverticulitis, tumors, and other disease entities for which resection is indicated. A systematic search is planned for detection of the antigen in all other bodily tissues that are available from biopsy and resection specimens. A search for neutralizing antibody in serum from a wide variety of populations is planned. Also more rapid methods for determining serum antibody will be sought, including microneutralization, complement fixation, hemagglutination-inhibition and plaque neutralization tests. Finally, to assess transmissibility, the antigen will be administered to experimental animals and local and systemic morphologic effects compared to those induced in animals injected with normal tissue.